The trial of Thomas Lubanga at the international criminal court in The Hague started in 2009. Photograph: Michael Kooren/REUTERS

Prosecutors on Thursday began wrapping up the international criminal court's landmark first trial by urging judges to convict a Congolese warlord of recruiting hundreds of child soldiers and sending them to fight and kill in his country's brutal conflict.

Deputy prosecutor Fatou Bensouda told judges that evidence in the trial, which began in 2009, gave voice to children that militia leader Thomas Lubanga had "transformed into killers; those girls that Mr Lubanga offered to his commanders as sexual slaves".

Bensouda said the armed wing of Lubanga's Union of Congolese Patriots political party trained hundreds of children in 20 camps scattered across the Ituri region of eastern Congo in 2002-2003.

"They were used to fight in conflicts. They were used to kill, rape and pillage," she said.

The actor Angelina Jolie, who is a goodwill ambassador for the UN high commissioner for refugees, was among dozens of people who watched proceedings from the court's public gallery.

Lubanga's defence lawyers are expected to tell judges on Friday that the prosecution evidence was flawed by false witness testimony and that Lubanga in fact tried to liberate child soldiers, not recruit them.

Lubanga's trial has been hailed as a significant step in the development of international law. It was the first international case to focus exclusively on child soldiers and the opening trial at the world's first permanent war crimes tribunal.

However it was overshadowed by delays and by friction between prosecutors and judges.

The trial was put on hold in June 2008 – 10 days before it was scheduled to start – when judges ruled that the prosecutor Luis Moreno-Ocampo had not given lawyers evidence that could have helped Lubanga. He refused to turn over some 200 documents because they came from organisations including the UN on condition that they not be disclosed to others.

Judges said the confidentiality agreements meant "the trial process has been ruptured to such a degree that it is now impossible to piece together the constituent elements of a fair trial".

Moreno-Ocampo eventually got consent from all the organisations and disclosed the material to defence lawyers, allowing the trial to get under way.

But judges halted it in July 2010 and ordered Lubanga's release when prosecutors defied a court order to reveal the identity of an intermediary who had helped them contact witnesses.

Prosecutors appealed against the decision and Lubanga remained in custody, but the incident underscored simmering tensions between prosecutors and the judges over disclosure of sensitive evidence.

Faced with the prospect of the case collapsing, prosecutors revealed the identity of their intermediary to the defence and appeals judges ruled that the trial could resume.

The tensions resurfaced on Thursday when the presiding judge, Adrian Fulford, refused to let Moreno-Ocampo answer a question addressed to one of his team of lawyers.

"Mr Ocampo can we please have some order," Fulford said. When Moreno-Ocampo tried again to answer Fulford sternly told the prosecutor: "Mr Ocampo, not at the moment."

Lubanga was arrested in March 2006 and was the first suspect to come into the custody of the international criminal court, which became operational in 2002.

The court has since issued indictments in high-profile conflicts such as the Darfur conflict in Sudan and the Gaddafi regime's brutal but unsuccessful campaign to stamp out dissent.

Lubanga is accused of leading a rebel group called the Union of Congolese Patriots which used child soldiers in savage fighting in the Ituri province in 2002-2003.

While welcoming his prosecution and the groundbreaking child soldier charges, human rights groups have criticised prosecutors for the narrow scope of the trial, saying they should also have charged him for the numerous rapes that victims say members of his militia perpetrated in a region notorious for widespread sexual violence.

"It was shocking to many of us that the announcement in 2006 of the case against Mr Lubanga did not include charges for such crimes and overlooked the suffering of thousands of women," said Brigid Inder, executive director of a group called Women's Initiatives for Gender Justice.

The UN special envoy for children in armed conflicts, Radhika Coomaraswamy, said leaders in conflict zones had often asked her about the ICC and the Lubanga prosecution. "I found that fear of the ICC a healthy development in international law," Coomaraswamy told the Associated Press. "Nobody can measure how many children have been saved because of deterrence. That's not something you can measure, but hopefully that will be the case."